This invention is directed to radiography. In particular, it is directed to a radiographic imaging assembly containing a radiographic silver halide film and a single fluorescent intensifying screen that provides improved medical diagnostic images of soft tissues such as in mammography.
The use of radiation-sensitive silver halide emulsions for medical diagnostic imaging can be traced to Roentgen""s discovery of X-radiation by the inadvertent exposure of a silver halide film. Eastman Kodak Company then introduced its first product specifically that was intended to be exposed by X-radiation in 1913.
In conventional medical diagnostic imaging the object is to obtain an image of a patient""s internal anatomy with as little X-radiation exposure as possible. The fastest imaging speeds are realized by mounting a dual-coated radiographic element between a pair of fluorescent intensifying screens for imagewise exposure. About 5% or less of the exposing X-radiation passing through the patient is adsorbed directly by the latent image forming silver halide emulsion layers within the dual-coated radiographic element. Most of the X-radiation that participates in image formation is absorbed by phosphor particles within the fluorescent screens. This stimulates light emission that is more readily absorbed by the silver halide emulsion layers of the radiographic element.
Examples of radiographic element constructions for medical diagnostic purposes are provided by U.S. Pat. No. 4,425,425 (Abbott et al.) and U.S. Pat. No. 4,425,426 (Abbott et al.), U.S. Pat. No. 4,414,310 (Dickerson), U.S. Pat. No. 4,803,150 (Kelly et al.), U.S. Pat. No. 4,900,652 (Kelly et al.), U.S. Pat. No. 5,252,442 (Tsaur et al.), and Research Disclosure, Vol. 184, August 1979, Item 18431.
While the necessity of limiting patient exposure to high levels of X-radiation was quickly appreciated, the question of patient exposure to even low levels of X-radiation emerged gradually. The separate development of soft tissue radiography, which requires much lower levels of X-radiation, can be illustrated by mammography. The first intensifying screen-film combination (imaging assembly) for mammography was introduced to the public in the early 1970xe2x80x2s. Mammography film generally contains a single silver halide emulsion layer and is exposed by a single intensifying screen, usually interposed between the film and the source of X-radiation. Mammography utilizes low energy X-radiation, that is radiation that is predominantly of an energy level less than 40 keV.
U.S. Pat. No. 6,033,840 (Dickerson) and U.S. Pat. No. 6,037,112 (Dickerson) describe asymmetric imaging elements and processing methods for imaging soft tissue.
Problem to be Solved
In mammography, as in many forms of soft tissue radiography, pathological features sought to be identified are often quite small and not much different in density than surrounding healthy tissue. Thus, relatively high average contrast, in the range of from 2.5 to 3.5, over a density range of from 0.25 to 2.0 is typical. Limiting X-radiation energy levels increases the absorption of the X-radiation by the intensifying screen and minimizes X-radiation exposure of the film, which can contribute to loss of image sharpness and contrast. Thus mammography is a very difficult task in medical radiography. In addition, microcalcifications must be seen when they are as small as possible to improve detection and treatment of breast cancers. As a result, there is desire to improve the image quality of mammography films. Improvements in image quality in imaging assemblies can be achieved by increasing the signal (that is, contrast) and modulating transfer function (MTF) and/or decreasing noise (reducing film/granularity and lowering quantum mottle). However, it would be desirable to achieve all of these results without the loss of other sensitometric properties.
This invention provides a solution to the noted problems with a radiographic imaging assembly comprising:
A) a radiographic silver halide film comprising a support having first and second major surfaces and that is capable of transmitting X-radiation, the radiographic silver halide film having a film speed of at least 100,
the radiographic silver halide film having disposed on the first major support surface, one or more hydrophilic colloid layers including at least one silver halide emulsion layer, and on the second major support surface, one or more hydrophilic colloid layers including at least one silver halide emulsion layer,
at least one of the silver halide emulsion layers comprising cubic silver halide cubic grains that have the same or different composition, and
B) arranged in association with the radiographic silver halide film, a single fluorescent intensifying screen that has a screen speed of at least 200 and comprises an inorganic phosphor capable of absorbing X-rays and emitting electromagnetic radiation having a wavelength greater than 300 nm, the inorganic phosphor being coated in admixture with a polymeric binder in a phosphor layer onto a flexible support and having a protective overcoat disposed over the phosphor layer.
Further, this invention provides a method of providing a black-and-white image comprising exposing the radiographic imaging assembly described above and processing the radiographic silver halide film, sequentially, with a black-and-white developing composition and a fixing composition, the processing being carried out within 90 seconds, dry-to-dry.
The present invention provides a means for providing radiographic images for mammography exhibiting improved image quality by increasing the radiographic signal while decreasing noise.
In addition, all other desirable sensitometric properties are maintained and the radiographic film can be rapidly processed in the same conventional processing equipment and compositions.
These advantages are achieved by using a novel combination of a radiographic film that has a film speed of at least 100 and a single fluorescent intensifying screen that has a screen speed of at least 200. Thus, while the imaging assembly of the present invention has an overall photographic speed that is comparable to known mammographic imaging assemblies, it provides improved image quality and processability.